Background: Globally, stigma continues to be a major barrier to engage and retain PLWH in care. The goal of this proposal is to understand the impact of multiple stigmas on antiretroviral (ART) initiation and retention in care among men who have sex with men (MSM) and transwomen (TW) living with HIV (MSM/TW+H) in India. India has the third largest HIV burden in the world, and the epidemic disproportionately impacts MSM/TW. Key (stigmatized) populations such as MSM/TW+H, are more likely to have poor HIV treatment outcomes, resulting in rates of ART initiation/retention and viral suppression that are unacceptably low to achieve UNAIDS 90-90- 90 goals. In India, MSM and TW women, though two distinct populations, face similar gender or sexual-identity and HIV-related stigmas, which may: (1) directly discourage HIV care engagement and (2) indirectly reduce capacity for HIV care engagement via mediators such as poor mental health (depression/anxiety), psychological resources (e.g. poor coping skills), and interpersonal factors (e.g. lack of social support). Studying stigma and its mediational paths to HIV outcomes are needed. Methods: This R21 study, responsive to PA 18-277,studies designed in partnership with service providers ... to understand factors impacting ART initiation... retention, is an innovative collaborative community research partnership with India's largest community-based HIV service provider. It is designed to leverage the agency's robust service and tracking infrastructure to conduct a longitudinal prospective cohort study of stigma, associated clinical outcomes (ART initiation and retention at 6 months), and potential mediators in 370 MSM-TW+H (185 MSM/TW each). Guided by the HIV Stigma Framework, our Aims are to: 1) Characterize the prevalence and change over time of multiple stigmas in a cohort of newly diagnosed Indian MSM/TW+H. This will also involve exploring potential differences in levels and types of stigmas between MSM and TW to inform future intervention development. 2) Examine the longitudinal direct and indirect (via mental health, interpersonal factors, and psychological resources) effects of stigmas on a) ART initiation by 3 months and b) retention in ART care at 6 months. We will also explore differences in the magnitude of effects across different stigmas for each outcome to better understand which are the strongest targets for future interventions. We will additionally conduct exploratory analyses to a) examine differences in these effects for MSM versus TW; and b) identify how future interventions can be tailored to meet the needs of each group. Potential Impact. While global health agencies are calling to reduce HIV and MSM/TW stigma, no effective and scalable interventions exist that address multiple stigmas among MSM/TW+H to improve HIV care continuum outcomes. This study will provide the needed empirical data about the multiple stigmas faced by MSM/TW+H, these stigmas' influence on ART initiation/retention, and potential modifiable factors (i.e. mediators) that could disrupt the impact of stigmas on HIV care and inform interventions.